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  • 1
    Publication Date: 2019-07-13
    Description: A global grid search is performed to find axi= and doubly=symmetric periodic orbits in the Restricted Three Body Problem using the dimensioned parameters associated with the Jupiter-Europa system.
    Keywords: Astrodynamics
    Type: 2005 AAS/AIAA Astrodynamics Specialist Conference; Aug 07, 2005 - Aug 11, 2005; Lake Tahoe, CA; United States
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  • 2
    Publication Date: 2019-07-13
    Description: This paper presents results from a study conducted at Goddard Space Flight Center (GSFC) to assess the real-time orbit determination accuracy of GPS-based navigation in a number of different high Earth orbital regimes. Measurements collected from a GPS receiver (connected to a GPS radio frequency (RF) signal simulator) were processed in a navigation filter in real-time, and resulting errors in the estimated states were assessed. For the most challenging orbit simulated, a 12 hour Molniya orbit with an apogee of approximately 39,000 km, mean total position and velocity errors were approximately 7 meters and 3 mm/s respectively. The study also makes direct comparisons between the results from the above hardware in-the-loop tests and results obtained by processing GPS measurements generated from software simulations. Care was taken to use the same models and assumptions in the generation of both the real-time and software simulated measurements, in order that the real-time data could be used to help validate the assumptions and models used in the software simulations. The study makes use of the unique capabilities of the Formation Flying Test Bed at GSFC, which provides a capability to interface with different GPS receivers and to produce real-time, filtered orbit solutions even when less than four satellites are visible. The result is a powerful tool for assessing onboard navigation performance in a wide range of orbital regimes, and a test-bed for developing software and procedures for use in real spacecraft applications.
    Keywords: Astrodynamics
    Type: ION 2005 National Technical Meeting; Jan 24, 2005 - Jan 26, 2005; Unknown
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  • 3
    Publication Date: 2019-07-13
    Description: Distant retrograde orbits (DROs) are stable periodic orbit solutions of the equations of motion in the circular restricted three body problem. Since no closed form expressions for DROs are known, we present methods for approximating a family of planar DROs for an arbitrary, fixed mass ratio. Furthermore we give methods for computing the first and second derivatives of the position and velocity with respect to the variables that parameterize the family. The approximation and derivative methods described allow a mission designer to target specific DROs or a range of DROs with no regard to phasing in contrast to the more limited case of targeting a six-state only.
    Keywords: Astrodynamics
    Type: AAS/AIAA Spaceflight Mechanics Meeting; Jan 22, 2006 - Jan 26, 2006; Tampa, FL; United States
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  • 4
    Publication Date: 2019-07-13
    Description: The hostile environment of third body perturbations restricts a mission designer's ability to find well-behaved reproducible capture trajectories when dealing with limited control authority as is typical with low-thrust missions. The approach outlined in this paper confronts this shortcoming by utilizing dynamical systems theory and an extensive preexisting database of Restricted Three Body Problem (RTBP) periodic orbits. The stable manifolds of unstable periodic orbits are utilized to attract a spacecraft towards Europa. By selecting an appropriate periodic orbit, a mission designer can control important characteristics of the captured state including stability, minimum altitudes, characteristic inclinations, and characteristic radii among others. Several free parameters are optimized in the non-trivial mapping from the RTBP to a more realistic model. Although the ephemeris capture orbit is ballistic by design, low-thrust is used to target the state that leads to the capture orbit, control the spacecraft after arriving on the unstable quasi-periodic orbit, and begin the spiral down towards the science orbit. The approach allows a mission designer to directly target fuel efficient captures at Europa in an ephemeris model. Furthermore, it provides structure and controllability to the design of capture trajectories that reside in a chaotic environment.
    Keywords: Astrodynamics
    Type: 2006 AAS/AIAA SpaceFlight Mechanics Meeting; Jan 22, 2006 - Jan 26, 2006; Tampa, FL; United States
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  • 5
    Publication Date: 2019-07-13
    Keywords: Astrodynamics
    Type: 2006 Global Trajectory Optimisation Workshop; Feb 02, 2006; Noordwijk; Netherlands
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  • 6
    Publication Date: 2019-07-13
    Description: A high degree and order Lunar gravitational field is superimposed on the Earth-Moon Restricted Three Body model to capture the dominating forces on a spacecraft in the vicinity of the Moon. For the synchronously rotating Moon, periodic orbits in this model map repeat ground tracks and represent higher order solutions to the frozen orbit problem. The near-circular, stable or near-stable solutions are found over a wide range of defining characteristics making them suitable for long-lifetime parking applications such as science orbits, crew exploration vehicle parking orbits, and global coverage constellation orbits. A full ephemeris is considered for selected orbits to evaluate the validity of the time-invariant, simplified model. Of the most promising results are the low-altitude families of near-circular, inclined orbits that maintain long-term stability despite the highly non-spherical Lunar gravity. The method is systematic and enables rapid design and analysis of long-life orbits around any tidally-locked celestial body with an arbitrarily high degree and order spherical harmonic gravity field. .
    Keywords: Astrodynamics
    Type: AIAA Paper 2006-6750 , AAS/AIAA Astrodynamics Specialist Conference; Aug 01, 2006; Keystone, CO; United States
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  • 7
    Publication Date: 2019-07-13
    Description: A global grid search is performed to find simply- and doubly-symmetric periodic orbits in the Restricted Three Body Problem using the dimensioned parameters associated with the Jupiter-Europa system.
    Keywords: Astrodynamics
    Type: 2005 AAS/AIAA Astrodynamics Specialist Conference; Aug 07, 2005 - Aug 11, 2005; Lake Tahoe, CA; United States
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